When faced with grossness at home (read: the whole house has the flu, or you found a cockroach infestation under the sink, or the dog trashed the room after eating who-knows-what), it’s tempting to bring out all of the big guns and throw every cleaning product you’ve got at the problem. But don’t!

First of all, most cleaning products are plenty effective on their own. Plus, combining them could be toxic—and in some cases lethal.

“Some people just think more product is better, but they don’t think about science and safety first,” says Nancy Bock of the American Cleaning Institute. “Mixing cleaning products can lead to irritated airways, respiratory problems, or burns to skin, eyes, throat, nose, and lungs. Some gases created from combined cleaning products could cause damage of the nervous system, eyes, lungs, skin, liver, kidneys, and even death.”

So good rule of thumb: “Don’t take any chances when it comes to safe use of products,” says Bock. Don’t believe us yet? Here are some tempting cleaning combos that are especially bad.

Hydrogen Peroxide + Vinegar

While these two chemicals can be used in succession as a cleaning duo, do not mix them together. “Combining these two creates peracetic acid or corrosive acid, an irritant that, in high concentrations, can harm the skin, eyes, throat, nose, and lungs,” says Bock.

Drain Cleaner + More Drain Cleaner

If you’ve got a clog, it’s tempting to pour in as much drain cleaner as you can find under your sink — but beware of using one right after the other, because these super-strong formulas (they’re meant to eat away those clogs!) can react very, very badly. “Combining drain cleaners can cause the release of chlorine gas and potentially lead to an explosion,” says Bock.

Bleach + Ammonia

Combining bleach and ammonia releases chloramine vapors, which can cause respiratory problems and throat burns if inhaled, says Bock. Beware that many cleaning products contain either bleach or ammonia in their formulas, so the fact that you could be combining these two might not be so obvious — which is why you should never, ever mix any kind of cleaning product.

Bleach + Rubbing Alcohol

This combination releases chloroform, a gas notorious for being used by old-fashioned bad guys to knock out their victims. High levels of exposure can lead to damage of the nervous system, eyes, lungs, skin, liver, kidneys, and even death. “Even low levels can make you dizzy or nauseous,” says Bock.

Bleach + Vinegar

Same deal: This releases chlorine and chloramine vapors. These can cause a chemical burn, most likely in your lungs or eyes,” says Bock.

The takeaway: Again, to be super clear, you should never mix cleaning supplies! It’s that simple.